Glutamate receptor expression regulates quantal size and quantal content at the Drosophila neuromuscular junction

At the Drosophila glutamatergic neuromuscular junction, the postsynaptic ce ll can regulate synaptic strength by both changing its sensitivity to neuro transmitter and generating a retrograde signal that regulates presynaptic t ransmitter release. To investigate the molecular mechanisms underlying thes e forms of plasticity, we have undertaken a genetic analysis of two postsyn aptic glutamate receptors that are expressed at this synapse. Deletion of b oth genes results in embryonic lethality that can be rescued by transgenic expression of either receptor. Although these receptors are redundant for v iability, they have important differences. By transgenically rescuing the d ouble mutant, we have investigated the relationship of receptor gene dosage and composition to synaptic function. We find that the receptor subunit co mposition regulates quantal size, Argiotoxin sensitivity, and receptor dese nsitization kinetics. Finally, we show that the activity of the receptor ca n regulate the retrograde signal functioning at this synapse. Thus, the div ersity of receptors expressed at this synapse provides the cell with mechan isms for generating synaptic plasticity.